Exergy valorization of a water electrolyzer and CO₂ hydrogenation tandem system for hydrogen and methane production

In this work, we introduce a water electrolysis and CO₂ hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO₂ hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy. A thermodynamic analysis of the tandem system was carried out. Our analysis exposes that it is possible to increase the exergy efficiency of the water electrolyzer and CO₂ hydrogenation system by thermal coupling, where the thermal energy required to split water into H₂ and O₂ during the electrolysis process is compensated by the heat generated during the CO₂ hydrogenation reaction. Here, the conditions at which high exergy efficiency can be achieved were identified.